Heretofore, polyimide films have been used in a variety of applications where heat resistance is an important requirement. The polyimide film is usually manufactured by casting a solution of a polyamic acid, which is a precursor of the polyimide, and treating the resulting film for solvent removal and dehydration for cyclization reaction.
However, the casting method involving the use of a solvent not only presents the environmental problems of pollutions and health hazard but is low in productivity, with the consequent high cost of production.
An object of the present invention is to provide a tubular thermoplastic polyimide film manufactured by the melt-extrusion of a molding compound composed predominantly of a thermoplastic polyimide resin.
An another object of the present invention is to provide a tubular thermoplastic polyimide film with improved dimensional accuracy, inclusive of the accuracy of film thickness.
Other objects and features of the invention will become apparent from the description of the invention which follows.